James,
I appreciate seeing some folks trying to build some sort of fallout shelter, as these may, unfortunately come in handy someday soon. Since I build these for a living, I thought I’d throw some basic suggestions out there for the readers. For simple fallout shelters, assuming that blast will not be a factor, above ground concrete walls should be 24 inches thick (or better if you can afford it!). Walls below grade can be a mere 10 inches thick. Ceilings: 24 inches will provide fair protection, assuming “rainout” does not occur in your locale. [The Swiss shelter building code calls for 30 inches, but public shelters average about a meter of concrete with a meter of earth on top] A rainout will cause a great deal of the fallout in a cloud that would have fallen to the ground hundreds of miles away to come down promptly, right on top of you, and it will be concentrated. Dose rates many times higher could result, rendering a marginal shelter totally ineffective (occupants will die).
We get calls from good folks who have designed and built a nice concrete garage with a shelter/basement. They usually call to order an air handler to round out their shelter. The first question I ask them is, “how thick is the ceiling?”. Most excitedly reply “eight inches!” My heart sinks, for they have expended a great deal of effort, time, and money to build a nice storage area…but it is totally unworkable as a fallout shelter. An eight inch concrete ceiling has a protection factor of about 12, at best. That is inadequate for even a mild dose of local fallout. Gamma rays are very penetrating, and heavy mass is require to defeat them, or reduce them to levels that can be managed by the body’s immune system. Twenty four inches of good concrete between fallout particles and shelter occupants will do a pretty good job, even it there happens to be a rainout. I’d be more inclined to push on the 30 inches if it were in my budget to do so.
Wood is an extremely poor shielding material, but earth is roughly half as good as concrete….and dirt cheap! If you can cover your shelter room with at least forty inches of earth, you’ll have a protection factor of one thousand…probably adequate for most folks. [Do not use wood in your shelter structure, as it will rot and become dangerous in a short period of time.] The shelters we build typically get buried with ten feet of earth, and have a protection factor of over a billion. But our shelters are designed to protect to within 1/2 mile of ground zero of the current heavy hitters in the Russian nuclear arsenal. Most folks living in a rural setting will not require this level of protection. If you can afford a good shelter, I think it’s a sound investment. For those on a tight budget, try to build something that has adequate mass in it that will not collapse. Don’t forget ventilation, sanitation, and a well-shielded entrance. As FEMA had a great deal of trouble delivering ice after a hurricane, it is clear that should a nuclear event occur here in America, we will be on our own. Plan, and build, accordingly. – Paul S.